Yes, this is a very newbish question but I cannot find the exact answer in the manual: What use are Armies before Corps are enabled, for countries other than France? Can they provide bonuses to Independent stacks nearby?

In the manual it is written that Armies cannot initiate battles by themselves:

An Army HQ with combat Units in reserve will react quickly to support Corps formations but should not be viewed as a combat Stack. It is important to note that a lone Army Stack will never initiate combat by itself.

For example, at the beginning of 1805 Russia can create two Armies in 1805, but no Corps. One is already created under Alexander, but I can create another. The reason is, what for if I cannot create Corps?

I am not sure I understand what you mean by "command control", game-wise. If I enter a battle with an Independent stack and a full-CP Army lays nearby, will the latter still march to the sound of guns? Will they still act as an operational reserve?

What is confusing to me is that Armies cannot initiate battle on their own. So if I put Divisions and Regiments into one and bring that Army to a border for a fight, these must get involved somehow...

Armies won't initiate offensive combat if accompanied by some other friendly stack in the region. They will defend normally.

If there are no other friendly stack in the region they will initiate combat normally, both offensive and defensive.I "think" friendly units inside a structure in the same region will not affect the army ability to initiate combat.. But I may be wrong in this last thing...Regards!